In courtrooms, eyewitness testimony is considered extremely powerful. But should it be? At TEDxUSC, forensic psychologist Scott Fraser explains why, even when witnesses feel sure they are telling a true story, or making the right identification, their minds could be playing tricks on them — filling in blanks in traumatic memories with erroneous information.

Fraser tells the story of Francisco Carrillo, who at age 17 was identified as the gunman in a drive-by shooting that left a man dead on the street in front of his teenage son and five friends. After maintaining his innocence for 20 years, Carrillo was released from jail in 2011. (Read the Los Angeles Times’ take on his release.) While all six teenage witnesses gave testimony that they had clearly seen Carrillo fire the gun from a moving car, a re-creation of the conditions of the shooting showed that it had been very dark, that few streetlights were on, and that shadows from the car would have made it impossible for anyone standing on the street to get a good look at the shooter’s face. The witnesses recanted their identifications.

As Fraser says, it wasn’t that the witnesses were lying. They were simply working from reconstructed memories.

“Under the best of observation conditions, we only detect, encode and store in our brains bits and pieces of the experience in front of us,” Fraser says. “We have a partial, incomplete story … The brain fills in information that was not originally stored, from inference, from speculation, from information that came to you after the observation.”

The brain’s tendency to reconstruct memory is one reason, Fraser says, that eyewitness testimony, though effective in courtrooms, is deeply problematic. He points to the work of The Innocence Project, an organization that works to exonerate wrongfully convicted people. Since 1992, it has cleared 297 people in the US, largely using DNA evidence. In three-quarters of cases, the conviction had hinged on eyewitness testimony alone.

(The New Jersey Supreme Court, thanks to this stat, instituted new rules in July, calling for judges to instruct juries that the “human memory is not foolproof.”)

Below, five other TED and TEDx speakers on wrongful convictions and general skews in our legal systems.

Bryan Stevenson: We need to talk about an injusticeThe United States has the highest incarceration rate in the world, says human rights lawyer Bryan Stevenson in this beautiful talk from TED2012. And our justice system cleaves a massive imbalance along racial and class lines. “We have a system of justice in this country that treats you much better if you’re rich and guilty than if you’re poor and innocent,” says Stevenson in this must-see talk.

Rob Warden: On false confessionsAs a founder of the Center of Wrongful Convictions at Northwestern University, Rob Warden is concerned with how frequently people confess to crimes they didn’t commit — because they were scared of being accused of something worse, because they thought they might have blocked the crime out of their memory, or because they feel desperate after hours of police questioning. At TEDxMidwest, Warden gives the shocking statistic that, in his county, nearly 50 percent of wrongful convictions to date involved a false confession.

Peter Donnelly: How stats fool juriesStatistics are often hard to understand. But when it’s an expert witness in a trial providing the faulty numbers, it can have a devastating impact. In this talk from TEDGlobal 2005, mathematician Peter Donnelly explains common misconceptions about statistics — and how a doctor giving a poorly calculated stat during a murder trail in England led to a woman’s wrongful conviction.

James Lockyer: Defending the wrongfully convictedJames Lockyer was a criminal lawyer for 15 years, until one case changed the course of his career. In this talk from TEDxIB@York, Lockyer tells the story of a client who had been wrongfully accused of rape and murder — and why the experience has led him to advocate against the death penalty.

David R. Dow: Lessons from death row inmatesLawyer David R. Dow has defended hundreds of death-row inmates, and has noticed that almost all of them share a similar biography — they come from highly dysfunctional homes and have had experience with the juvenile justice system. In this talk from TEDxAustin, Dow focuses on what could be done to help young people before they commit a violent crime — challenging society to intervene in troubled life stories.

How do you keep memories? And how much can you trust those preservations? This week’s TED Radio Hour, “Memory Games,” looks at recollections versus actual experiences, sorts through our tendency to create false memories, and unpacks how we can actually enhance our ability to remember. Forensic psychologist Scott Fraser starts the hour. He is the […]

Elizabeth Loftus begins her talk at TEDGlobal 2013 with the tragic story of Steve Titus, who was arrested in 1980 because he sort of matched the physical description of, and drove a similar car to, a man who had raped a woman in his area. Looking at a photo lineup, the victim told police that […]